(1) Field of the Invention
The present invention relates to ceramic rotors having a honeycomb structure for use in pressure wave superchargers and a process for producing the same.
More particularly, the invention relates to ceramic rotors suitably used for pressure wave superchargers in automobiles and production thereof (The ceramic honeycomb structures are used herein to mean a structure made of a ceramic material in which a plurality of through holes are defined by partition walls).
(2) Related Art Statement
Most pressure wave superchargers used in internal combustion engines in automobiles and the like have been rotors made of metallic materials. For instance, such rotors have been produced from an iron-cobalt-nickle alloy material according to a precision casting based on a lost wax process.
However, rotors for pressure wave superchargers require properties such as light weight, low thermal expansion, heat resistance, high strength, and low cost. It is difficult to attain all such properties when metallic materials are employed. Thus, a new process for producing rotors to be used in pressure wave superchargers by using new materials has been demanded.
Incidentally, rotors made of metallic materials for use in pressure wave superchargers intrinsically have a great apparent density of about 8 g/cc, so that the weight of the rotors is great. Thus, such rotors unfavorably need to be rotated by using belts because they cannot be rotated by an energy of waste gases from an engine. Further, their coefficient of thermal expansion is relatively large due to the metallic materials so that it is difficult to lessen a clearance at opposite axial ends of the rotor assembled into the supercharger between the rotor and a housing. Consequently, supercharging performance is undesirably damaged due to gas leakage. Further, since metallic rotors for use in pressure wave superchargers have a smaller strength per unit weight, it is difficult to make the thickness of cell walls smaller. Even if cells can be formed in two concentric annular rows, it is impossible that cells are formed in a concentrical arrangement consisting of three or more annular rows effective for reduction of noises because such an arrangement leads to weight increase.
Further, since metallic rotors for use in pressure wave superchargers have an upper tolerable limit for the maximum waste gas temperature, some limitation is necessary for a combustion temperature which effectively increases the efficiency of an engine output.